Pressure sensitive adhesives typically include materials (e.g., elastomers) that are either inherently tacky or that are tackified with the addition of tackifying resins. They can be defined by the Dahlquist criteria described in Handbook of Pressure Sensitive Adhesive Technology, D. Satas, 2nd ed., page 172 (1989) at use temperatures. This criterion defines a good pressure sensitive adhesive as one having a 1 second creep compliance of greater than 1xc3x9710xe2x88x926 cm2/dyne. Alternatively, since modulus is, to a first approximation, the inverse of compliance, pressure sensitive adhesives may be defined as adhesives having a modulus of less than 1xc3x97106 dynes/cm2.
Another well-known means of identifying a pressure sensitive adhesive is that it is aggressively and permanently tacky at room temperature and firmly adheres to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure as described in xe2x80x9cGlossary of Terms Used in the Pressure Sensitive Tape Industryxe2x80x9d provided by the Pressure Sensitive Tape Council, August, 1985.
Another suitable definition of a pressure sensitive adhesive is that it preferably has a room temperature storage modulus within the area defined by the following points as plotted on a graph of modulus versus frequency at 25xc2x0 C.: a range of moduli from approximately 2xc3x97105 to 4xc3x97105 dynes/cm2 at a frequency of approximately 0.1 radian/second (0.017 Hz), and a range of moduli from approximately 2xc3x97106 to 8xc3x97106 dynes/cm2 at a frequency of approximately 100 radians/second (17 Hz) (for example, see FIGS. 8-16 on p. 173 Handbook of Pressure Sensitive Adhesive Technology, D. Satas, 2nd ed., (1989)).
Other methods of identifying a pressure sensitive adhesive are also known. Any of these methods of identifying a pressure sensitive adhesive may be used to identify suitable pressure sensitive adhesives of the present invention.
There is an ongoing need to modify pressure sensitive adhesives to meet the criteria for new applications. In general, additives may be used to modify adhesives; however, when additives are incorporated into pressure sensitive adhesives to modify their properties, care must be taken to avoid a loss in peel adhesion or shear strength.
Major classes of pressure sensitive adhesives include acrylics, polyurethanes, poly-alpha-olefins, silicones, and tackified natural and synthetic rubbers. Some examples of synthetic rubbers include tackified linear, radial (e.g., star), tapered, and branched styrenic block copolymers, such as styrene-butadiene-styrene, styrene-ethylene/butylene-styrene, and styrene-isoprene-styrene. Uncrosslinked acrylics typically have good low temperature adhesion but poor shear strength. Block copolymer adhesives have good shear strength and adhesion at room temperature, but poor adhesion at non-ambient temperatures, and poor shear strength at elevated temperatures.
Generally, when additives are used to alter properties of pressure sensitive adhesives, the additives should be miscible with the pressure sensitive adhesive or form homogeneous blends at the molecular level. Some types of pressure sensitive adhesives have been modified with tackified thermoplastic elastomers (e.g., styrene-isoprene-styrene block copolymers), thermoplastics (e.g., polystyrene, polyethylene, or polypropylene), and elastomers (e.g., polyolefins, natural and synthetic rubbers). For example, thermoplastic materials have been added to acrylic pressure sensitive adhesives. Such materials are described in International Publication Nos. WO 97/23577, WO 95/25469 (all to Minnesota Mining and Manufacturing Co.) as having a substantially continuous domain and a substantially fibrillous to schistose domain. Although such pressure sensitive adhesives are described as having increased peel adhesion relative to the acrylic component or solvent-coated blends of the same components, there is still a need for adhesives exhibiting useful combinations of properties (i.e., peel, shear, clean removal, etc.), particularly at high and low temperatures (i.e., non-ambient temperatures).
The present invention is directed to pressure sensitive adhesive compositions that include at least one acrylate pressure sensitive adhesive component and at least one thermoplastic elastomer-based pressure sensitive adhesive component. The acrylate pressure sensitive adhesive component includes at least one polymerized monofunctional (meth)acrylic acid ester monomer having a Tg (glass transition temperature) of no greater than about 0xc2x0 C. when homopolymerized, and 0 to about 10 wt % of at least one copolymerized monofunctional ethylenically unsaturated monomer having a Tg of at least about 10xc2x0 C. when homopolymerized. The thermoplastic elastomer-based pressure sensitive adhesive component includes a radial block copolymer, and preferably, a tackifying agent. In certain preferred embodiments, the pressure sensitive adhesive composition is crosslinked. This can occur through crosslinking of the individual components or upon crosslinking the composition after combining the individual components.
As used herein, a thermoplastic elastomer (i.e., thermoplastic rubber) is a polymer having at least two homopolymeric blocks or segments, wherein at least one block has a Tg of greater than room temperature (i.e., about 20xc2x0 C. to about 25xc2x0 C.) and at least one block has a Tg of less than room temperature. In a thermoplastic elastomer these two blocks are generally phase separated into one thermoplastic glassy phase and one rubbery elastomeric phase. A radial block copolymer is a polymer having more than two arms that radiate from a central core (which can result from the use of a multifunctional coupling agent, for example), wherein each arm has two or more different homopolymeric blocks or segments as discussed above. See, for example, the Handbook of Pressure Sensitive Adhesive Technology, D. Satas, 2nd ed., Chapter 13 (1989).
Significantly, the present invention provides adhesives with one or more of the following: good low temperature adhesion, high temperature shear strength, clean removal after high temperature applications, and good lifting resistance as measured by low stress peel. Particularly preferred adhesives have all of these properties. In a preferred embodiment, an adhesive tape sample that includes a backing and the pressure sensitive adhesive composition disposed thereon has a peel adhesion value from a glass substrate of at least about 22 Newtons/decimeter (N/dm) at 4xc2x0 C. and a shear strength value from stainless steel of at least about 100 minutes at 71xc2x0 C.
In a preferred embodiment, the present invention provides a crosslinked pressure sensitive adhesive composition that includes at least one crosslinked acrylate pressure sensitive adhesive component and at least one thermoplastic elastomer-based pressure sensitive adhesive component. The thermoplastic elastomer-based pressure sensitive adhesive component includes an asymmetric radial block copolymer of the general formula QnY wherein Q represents an arm of the asymmetric radial block copolymer and has the formula S-B, n preferably represents the number of arms and is a whole number of at least three, Y is the residue of a multifunctional coupling agent, S is a thermoplastic polymer segment, and B is an elastomeric polymer segment.
Adhesive articles are also provided by the present invention. Such articles include a substrate (i.e., backing) having the pressure sensitive adhesive composition described herein disposed thereon.
Pressure sensitive adhesive compositions of the present invention are suitable for use in a variety of applications, preferably over a broad temperature range (e.g., about 4xc2x0 C. to about 93xc2x0 C.). These adhesives include a unique combination of an acrylate pressure sensitive adhesive component and a thermoplastic elastomer-based pressure sensitive adhesive component. Each of these components is a pressure sensitive adhesive with advantageous properties individually, but when combined result in pressure sensitive adhesive compositions that can be used to provide adhesive articles (e.g., tapes) that demonstrate one or more of the following properties: good low temperature adhesion; good high temperature shear strength; clean removal after high temperature applications; and good lifting resistance as measured by low stress peel. Particularly preferred adhesives of the present invention have all of these properties.
The acrylate pressure sensitive adhesive component includes at least one polymerized monofunctional (meth)acrylic acid ester monomer having a Tg of no greater than about 0C. when homopolymerized, and preferably, at least one copolymerized monofunctional ethylenically unsaturated monomer having a Tg of at least about 10xc2x0 C. when homopolymerized, which is optionally present in an amount of no greater than about 10 wt %. The thermoplastic elastomer-based pressure sensitive adhesive component includes a radial block copolymer, and preferably, a tackifying agent. Although International Publication Nos. WO 97/23577, WO96/25469 (all to Minnesota Mining and Manufacturing Co.) generally encompass such pressure sensitive adhesive compositions, there is no specific recognition of the advantages of the combination of these particular components, particularly for use in applications at high and low temperatures.
Pressure sensitive adhesive compositions of the present invention exhibit room temperature (e.g., 21xc2x0 C.) peel adhesion values that are sufficient for many applications, even after high humidity aging. Significantly, pressure sensitive adhesive compositions of the present invention provide adhesive articles that preferably have a peel adhesion value of at least about 22 N/dm (20 ounces/inch, oz/in), more preferably, at least about 33 N/dm (30 oz/in), and most preferably, at least about 44 N/dm (40 oz/in), at 4xc2x0 C. These values are typically determined according to the test procedure described herein using a glass substrate and an adhesive tape sample that includes a cloth backing laminated with polyethylene (although it is believed that such results can be obtained using other backings) and a 125 xcexcm (5.0 mils) thick layer of the pressure sensitive adhesive composition disposed thereon.
Pressure sensitive adhesive compositions of the present invention exhibit room temperature (e.g., 21xc2x0 C.) shear strength values that are sufficient for many applications. Significantly, pressure sensitive adhesive compositions of the present invention provide adhesive articles that preferably have a shear value of at least about 100 minutes, and more preferably, at least about 1000 minutes, at 71xc2x0 C. These values are typically determined according to the test procedure described herein using a stainless steel substrate and an adhesive tape sample that includes a cloth backing laminated with polyethylene (although it is believed that such results can be obtained using other backings) and a 125 xcexcm (5.0 mils) thick layer of the pressure sensitive adhesive composition disposed thereon.
Pressure sensitive adhesive compositions of the present invention exhibit room temperature (e.g., 21xc2x0 C. ) removability that is sufficient for many applications. Significantly, pressure sensitive adhesive compositions of the present invention provide adhesive articles that preferably leave no greater than about 10% residue (by area), and more preferably, no greater than about 5% residue (by area), upon removal from a substrate after 30 minutes at 93xc2x0 C. These values are typically determined according to the test procedure described herein using a painted cold rolled steel panel and an adhesive tape sample that includes a cloth backing laminated with polyethylene (although it is believed that such results can be obtained using other backings) and a 125 xcexcm (5.0 mils) thick layer of the pressure sensitive adhesive composition disposed thereon.
Pressure sensitive adhesive compositions of the present invention provide adhesive articles that preferably have a low stress peel of at least about 300 minutes, and more preferably, at least about 1000 minutes. This is a measure of the lifting resistance of the adhesive articles. These values are typically determined according to the test procedure described herein using a stainless steel substrate and an adhesive tape sample that includes a cloth backing laminated with polyethylene (although it is believed that such results can be obtained using other backings) and a 125 xcexcm (5.0 mils) thick layer of the pressure sensitive adhesive composition disposed thereon.
Preferably, pressure sensitive adhesive compositions of the present invention include about 10 weight percent (wt %) to about 90 wt %, and more preferably, about 30 wt % to about 70 wt % of the acrylate pressure sensitive adhesive component. Preferably, the pressure sensitive adhesive of the present invention includes about 10 wt % to about 90 wt %, and more preferably, about 30 wt % to about 70 wt %, of the thermoplastic elastomer-based pressure sensitive adhesive component.
Useful acrylic (i.e., acrylate) pressure sensitive adhesive materials include those having a major amount (e.g., at least about 90 weight percent) of at least one polymerized has monofunctional (meth)acrylic acid ester whose homopolymer has a Tg of no greater than about 0xc2x0 C., and optionally, at least one copolymerized monofunctional ethylenically unsaturated monomer whose homopolymer has a Tg (glass transition temperature) of at least about 10xc2x0 C. The monofunctional ethylenically unsaturated monomer is optionally present in an amount of no greater than about 10 wt %, and preferably no greater than about 5 wt %. Included within the scope of the present invention are acrylate pressure sensitive adhesives that have none of this monomer present, although it is preferably present.
The monofunctional (meth)acrylic acid ester is preferably an ester of a nontertiary alcohol in which the alkyl group contains at least about 3 carbon atoms (on average), and preferably about 4 to about 14 carbon atoms (on average). Typically, the homopolymers of such monomers have a Tg of no greater than about 0xc2x0 C. The alkyl group of the nontertiary alcohol can optionally contain oxygen atoms in the chain, thereby forming ethers, for example.
The term xe2x80x9c(meth)acrylicxe2x80x9d as used in this context refers to acrylic and methacrylic. The term xe2x80x9cmonofunctionalxe2x80x9d as used in the context of a xe2x80x9cmonofunctional (meth)acrylic acid esterxe2x80x9d refers to a mono-(meth)acrylic monomer or a monomer containing one (meth)acrylic functionality, although other functionality can be present. The term xe2x80x9cmonofunctionalxe2x80x9d as used in the context of a xe2x80x9cmonofunctional ethylenically unsaturated monomerxe2x80x9d refers to a monoethylenically unsaturated monomer or a monomer containing one ethylenically unsaturated functionality, although other functionality can be present.
Examples of classes of suitable monofunctional (meth)acrylic acid esters include, but are not limited to, 2-methylbutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, lauryl acrylate, n-decyl acrylate, 4-methyl-2-pentyl acrylate, isoamyl acrylate, sec-butyl acrylate, and isononyl acrylate. Preferred (meth)acrylic acid esters that can be used include, but are not limited to, 2-ethylhexyl acrylate, isooctyl acrylate, lauryl acrylate, and 2-methylbutyl acrylate. Various combinations of such monomers can be employed.
Examples of suitable monofunctional ethylenically unsaturated monomers include, but are not limited to, (meth)acrylic acid, a (meth)acrylamide, a (meth)acrylate, an alpha-olefin, a vinyl ether, an allyl ether, a styrenic monomer, or a maleate. Examples of suitable monofunctional ethylenically unsaturated monomers include, but are not limited to, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, 2-hydroxyethyl acrylate or methacrylate, cyclohexyl acrylate, t-butyl acrylate, phenyl acrylate, isobornyl acrylate, 2-phenoxyethyl acrylate, N-vinyl pyrrolidone, N-vinyl caprolactam, acrylamide, methacrylamide, N-substituted and N,N-disubstituted acrylamides such as N-ethyl acrylamide, N-hydroxyethyl acrylamide, N-octyl acrylamide, N-t-butyl acrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide, and N-ethyl,N-dihydroxyethyl acrylamide. Preferred monofunctional ethylenically unsaturated monomers include, but are not limited to, acrylic acid, t-butyl acrylate, N,N-dimethyl acrylamide, N-octyl acrylamide, isobornyl acrylate, norbornyl acrylate, and 2-phenoxyethyl acrylate. A particularly preferred such monomer is acrylic acid. Various combinations of such monomers can be employed.
The acrylate pressure sensitive adhesive component of the pressure sensitive adhesive composition of the present invention can be crosslinked if desired. Crosslinking can be achieved to employed chemical crosslinks (e.g., covalent bonds or acid-base interactions) and/or physical crosslinks (e.g., from the formation of reinforcing domains due to phase separation). Crosslinking can be achieved by thermal crosslinking agents such as a multifunctional aziridine (e.g., 1,1xe2x80x2-(1,3-phenylene dicarbonyl)-bis-(2-methylaziridine) or xe2x80x9cbisamidexe2x80x9d); UV-crosslinking agents such as monoethylenically unsaturated aromatic ketone monomers free of ortho-aromatic hydroxyl groups (e.g., acryloxybenzophenone, para-acryloxyethoxybenzophenone, acrylated anthraquinones); high Tg macromers such as those that include vinyl functionality and are based upon poly(styrene) or poly(methyl methacrylate) and which are often referred to as a macromolecular monomer or macromer; metal crosslinkers (e.g., zinc oxide, zinc ammonium carbonate, zinc stearate); high energy electromagnetic radiation such as gamma or e-beam radiation; and/or the pendant acid and base groups. Suitable crosslinking agents are disclosed in U.S. Pat. No. 4,379,201 (Heilmann et al.), U.S. Pat. No. 4,737,559 (Keller et al.), U.S. Pat. No. 5,506,279 (Babu et al.), and U.S. Pat. No. 4,554,324 (Husman et al.). Various combinations of crosslinking agents can also be employed.
Exemplary acrylate pressure sensitive adhesives include those described in U.S. Pat. No. 4,693,776 (Krampe et al.). Other suitable acrylate pressure sensitive adhesives are described in U.S. Pat. Nos. 5,804,610 (Hamer et al.), U.S. Pat. No. 4,833,179 (Young et al.), and RE 24,906 (Ulrich).
The acrylate pressure sensitive adhesive component of the pressure sensitive adhesive composition of the present invention may be inherently tacky or tackified. Preferably, for use in the present invention they are inherently tacky. Useful tackifiers for acrylates include rosin esters, aromatic resins, aliphatic resins, and terpene resins.
The acrylate pressure sensitive adhesive component can be made using a variety of polymerization methods, including solution polymerization, emulsion polymerization, and solventless polymerization. As is known to one of skill in the art, thermal or photoinitiators may be employed in such methods. Suitable methods include those described in U.S. Pat. No. 4,181,752 (Martens et al.), U.S. Pat. No. 4,833,179 (Young et al.), U.S. Pat. No. 5,804,610 (Hamer et al.), U.S. Pat. No. 5,382,451 (Johnson et al.), U.S. Pat. No. 4,619,979 (Kotnour et al.), U.S. Pat. No. 4,843,134 (Kotnour et al.), and U.S. Pat. No. 5,637,646 (Ellis).
The thermoplastic elastomer-based pressure sensitive adhesive component includes a radial block copolymer having more than two arms, and preferably, a radial block polymer having at least three arms, more preferably, at least five arms, and most preferably, at least ten arms. A preferred radial block copolymer is a block copolymer of the general formula QnY wherein Q represents an arm of the block copolymer and has the formula S-B, n represents the number of arms and is preferably a whole number of at least three, Y is the residue of a multifunctional coupling agent, S is a thermoplastic polymer segment, and B is an elastomeric polymer segment.
Particularly preferred radial block copolymers of this general formula are asymmetric (i.e., the arms of the block copolymers are not all identical) and are described in U.S. Pat. Nos. 5,393,787 and 5,296,547 (both to Nestegard et al.). Preferred such asymmetric radial block copolymers have the above formula wherein S is a thermoplastic polymer segment endblock of a polymerized monovinyl aromatic homopolymer, preferably with at least two different molecular weight endblocks in the copolymer (e.g., one of about 5000 to about 50,000 number average molecular weight and one of about 1000 to about 10,000 number average molecular weight), and B is an elastomeric polymer segment midblock which connects each arm to the residue of a multifunctional coupling agent and includes a polymerized conjugated diene or combination of conjugated dienes.
Such radial block copolymers can be made by conventional block copolymer polymerization methods, such as a sequential addition anionic polymerization method described in U.S. Pat. Nos. 5,393,787 and 5,296,547 (both to Nestegard et al.). This polymerization method includes the formation of a living polymer of the general structure S-B-M, wherein M is a Group I metal such as Na, Li, or K. The living polymer is then coupled with a multifunctional coupling agent to form a linked block copolymer. Since this coupling reaction may not always go to completion, there may also be some unlinked diblock (S-B) present in the polymer mass. The amount of such unlinked diblock will vary with the coupling efficiency of the linking reaction, and can be as much as 70 wt %, but preferably no more than about 30 wt %, (based on the total weight of the radial block copolymer) of the diblock in the polymer mass.
The monomers that form the polymerized monovinyl aromatic endblocks typically contain about 8 to about 18 carbon atoms. Examples of such monomers include, but are not limited to, styrene, alpha-methylstyrene, vinyltoluene, vinylpyridine, ethylstyrene, t-butylstyrene, isopropylstyrene, dimethylstyrene, and other alkylated styrenes. The monomers that form the polymerized conjugated diene midblocks typically contain about 4 to about 12 carbon atoms. Examples of such monomers include, but are not limited to, butadiene, isoprene, ethylbutadiene, phenylbutadiene piperylene, dimethylbutadiene, ethylhexadiene, and hexadiene. The multifunctional coupling agents suitable for the block copolymer may be any of the polyalkenyl coupling agents or other materials known to have functional groups that can react with carbanions of the living polymer to form linked polymers. Examples of such coupling agents include, but are not limited to, silyl halides, polyepoxides, polyisocyanates, polyketones, polyanhydrides, and aliphatic, aromatic, or heterocyclic polyalkenyls.
The thermoplastic elastomer-based pressure sensitive adhesive component of the pressure sensitive adhesive composition of the present invention typically requires the presence of a tackifying agent (i.e., tackifier). Useful tackifiers include rosin and rosin derivatives, polyterpenes, coumarone indenes, hydrogenated resins, and hydrocarbon resins. Examples include, but are not limited to, alpha pinene-based resins, beta pinene-based resins, limonene-based resins, piperylene-based hydrocarbon resins, esters of rosins, polyterpene and aromatic modified polyterpene resins, aromatic modified piperylene-based hydrocarbon resins, aromatic modified dicyclopentadiene-based hydrocarbon resins, and aromatic modified co-terpene and ter-terpene resins.
The thermoplastic elastomer-based pressure sensitive adhesive component of the pressure sensitive adhesive composition of the present invention can be crosslinked if desired. Crosslinking can be achieved using high energy electromagnetic radiation such as gamma or e-beam radiation, for example. Alternatively, crosslinking can be achieved using a crosslinking agent such as a sulfur, a sulfur-donor, or peroxide curing systems traditionally used for crosslinking unsaturated rubbers. Other means of crosslinking include the use of reactive phenolic resins in combination with a metal catalyst, or the use of a multifunctional acrylate with a photoinitiator and ultraviolet light. Various combinations of crosslinking agents can also be employed.
Plasticizers may also be added to modify the properties of the thermoplastic elastomer-based pressure sensitive adhesive component, such as, for example, conformability or low temperature adhesion.
The acrylate pressure sensitive adhesive component and the thermoplastic elastomer pressure sensitive adhesive component are combined typically using melt extrusion techniques, as described in International Publication Nos. WO 97/23577, WO 96/25469 (all to Minnesota Mining and Manufacturing Co.). Mixing can be done by a wide variety of methods known to those of skill in the art that result in a substantially homogeneous distribution of the components. This can include dispersive mixing, distributive mixing, or a combination thereof. Both batch and continuous methods of mixing can be used. Preferably, the components are combined and the compositions are melt processed prior to crosslinking, if crosslinking is performed. Details of preparation of the compositions of the present invention are described in the examples.
In addition to the additives discussed above, others can be included in each individual pressure sensitive adhesive component of the pressure sensitive adhesive composition of the present invention, or added at the time of mixing the components, to adjust the properties of the adhesive. Such additives include compatibilizing materials, pigments, glass or polymeric bubbles or beads (which may be expanded or unexpanded), fibers, reinforcing agents, hydrophobic and hydrophilic silica, toughening agents, fire retardants, antioxidants, finely ground polymeric particles such as polyester, nylon, and polypropylene, and stabilizers. The additives are added in amounts sufficient to obtain the desired end-use properties.
Typically, and preferably, the pressure sensitive adhesive composition of the present invention is crosslinked after mixing the two major components. Crosslinking can be achieved using high energy electromagnetic radiation such as gamma or e-beam radiation, for example. Alternatively, crosslinking can be achieved after the components are combined using crosslinking agents such as those described above for crosslinking the individual pressure sensitive adhesive components. Various combinations of crosslinking agents can also be employed.
The adhesive compositions of the present invention can be applied to a substrate by a variety of coating methods, including batch and continuous coating hot melt coating methods, as described in International Publication Nos. WO 97/23577, WO 96/25469 (all to Minnesota Mining and Manufacturing Co.). The pressure sensitive adhesive compositions can be solidified by quenching using both direct methods, such as chill rolls or water baths, and indirect methods, such as air or gas impingement. The thickness of the layer of adhesive may vary over a broad range, such as from about 10 microns (xcexcm) to several hundred microns.
The substrates (i.e., backings) on which the pressure sensitive adhesive compositions can be disposed include, but are not limited to, cloth (e.g., cotton or fabric available under the trade designation RAYON), metallized films and foils, polymeric films, nonwoven polymeric materials, paper, foam backings, etc. Polymeric films include, but are not limited to, polyolefins such as polypropylene, polyethylene, low density polyethylene, linear low density polyethylene and high density polyethylene, polyesters, polycarbonates, cellulose acetates, polyimides, etc. Nonwovens include, but are not limited to, nylon, polypropylene, ethylene-vinyl acetate, polyurethane, etc. Foam backings include, but are not limited to, acrylic, silicone, polyurethane, polyethylene, polypropylene, neoprene rubber, etc. The substrates can be layered or made of composite materials if desired. For example, a preferred backing, is a cloth backing laminated to polyethylene.
Once the adhesive composition has been coated, and optionally crosslinked, the adhesive surface of the article may, optionally, be protected with a temporary, removable release liner (i.e., protective liner) such as a polyolefin (e.g., polyethylene or polypropylene) or polyester (e.g., polyethylene terephthalate) film, or a plastic film. Such films may be treated with a release material such as silicones, waxes, fluorocarbons, and the like.
The pressure sensitive adhesive compositions of the present invention can be used in a wide variety of adhesive articles, including medical tapes, sealing tapes, electrical tapes, repositionable tapes, die-cut graphics, wall decoration films, and particularly in removable tapes, such as masking tapes, sheets, and drapes.
Room and Low Temperature Peel Adhesion Tests
Pressure sensitive adhesive (PSA) tape samples, measuring 1.25 cm (width)xc3x9715 cm (length), were conditioned for greater than 24 hours at approximately 21xc2x0 C. and 50% relative humidity. These were then tested for peel adhesion from a clean glass substrate after exposure at one of two different conditions. Under the first condition (Room Temperature Peel Adhesion), the tape sample was adhered to the test substrate surface using one pass of a 2.1 kilogram (g) rubber-faced roller and tested using a Model 3M90 Slip/Peel tester (from IMASS, Inc., Accord, Massachusetts) at an angle of 180xc2x0 at a peel rate of 228.6 centimeters/minute (cm/min) all at a temperature of approximately 70xc2x0 F. (21xc2x0 C.) and 50% Relative Humidity. Under the second condition (Low Temperature Peel Adhesion) the tape sample, substrate, and peel tester were conditioned for 24 hours at a temperature of approximately 40xc2x0 F. (4xc2x0 C.) and tested at a temperature of approximately 40xc2x0 F. (4xc2x0 C.) using the method described above.
Peel Adhesion After High Humidity Aging Test
Pressure sensitive adhesive tape samples were conditioned and tested as described above with the following modifications. The substrate was clean stainless steel, the PSA tape was adhered to the substrate surface using four passes of a 2.1-kg rubber-faced roller after both were first conditioned at 70xc2x0 F. (21xc2x0 C.) and 50% Relative Humidity for more than 24 hours. The taped substrate was aged at 70xc2x0 F. (21xc2x0 C.) and 90% Relative Humidity for 24 hours then removed and stored at 70xc2x0 F. (21xc2x0 C.) and 50% Relative Humidity for 1 hour before measuring peel adhesion strength at 70xc2x0 F. (21xc2x0 C.).
Room and Elevated Temperature Shear Strength Tests
Shear strength, as determined by holding time, was measured on PSA tape samples at both room and elevated temperatures. A roll of the tape sample was conditioned for greater than 24 hours at approximately 21xc2x0 C. and 50% relative humidity. These were then tested for shear strength from a clean stainless steel substrate. The tape samples, measuring 12.5 cm (width)xc3x9725 cm (length), were adhered to the test substrate surface using four passes of a 2.1-kg rubber-faced roller. For testing at room temperature (70xc2x0 F., 21xc2x0 C.) the taped substrate was placed in a vertical holding rack and a static 500-gram load was attached to the tape at an angle of 180 degrees, and the time it took for the load to drop was measured in minutes. For testing at 160xc2x0 F. (71xc2x0 C.), the taped substrates were placed in a holding rack and conditioned at that temperature for 15 minutes before a 500-gram weight was hung from each sample. At both test temperatures the time it took for the weight to drop was recorded in minutes. For those samples still adhering to the substrate after 4000 minutes, the test was discontinued.
Low Stress Peel Adhesion Strength
Low stress peel adhesion strength, as determined by holding time, was measured on PSA tape samples at room temperature (70xc2x0 F., 21xc2x0 C.). The tape sample (in roll form) and stainless steel substrate were conditioned for greater than 24 hours at approximately 21xc2x0 C. and 50% relative humidity. The tape sample was then tested for low stress peel adhesion strength from a clean, 10.2 cm long stainless steel substrate. The tape sample, measuring 1.90 cm (width)xc3x9710.2 cm (length), was adhered to the stainless steel substrate using four passes of a 2.1-kg rubber-faced roller. The taped substrate was placed on the bottom side of a horizontal holding rack with the taped side facing down and a static load of 200 grams was attached to the tape at an angle of 90 degrees. The time it took for the load to drop was measured in minutes. For those samples still adhering to the substrate after 5500 minutes, the test was discontinued.
Removability After Temperature Aging rolled steel panel after aging at elevated temperature was determined by observing the amount of residual adhesive present upon removal of the tape after exposure to 200xc2x0 F. (93xc2x0 C.) for 30 minutes. The tape sample (in roll form) and painted cold rolled steel substrate (ACT Cold Rolled Steel B952 P60 DIW; Unpolish Topcoat AG129W1133 White, available as AIN100253 from ACT Laboratories, Incorporated, Hillsdale, Mich.) were conditioned for greater than 24 hours at approximately 70xc2x0 F. (21xc2x0 C.) and 50% relative humidity. The tape sample, measuring 1.27 cm (width)xc3x9710.2 cm (length), was then adhered to the painted cold rolled steel substrate, which measured 10.2 cm (width)xc3x9720.3 cm (length)xc3x970.08 cm (thickness), using four passes of a 2.1-kg rubber-faced roller. The taped substrate was placed in an oven preheated to 200xc2x0 F. (93xc2x0 C.) for 30 minutes. After 30 minutes, the oven door was opened and a 5.1-cm length of the tape was immediately peeled off the hot substrate by hand at an angle of 180 degrees. The partially detaped substrate was then removed from the oven, allowed to cool to room temperature in a controlled environment having a temperature of approximately 21xc2x0 C. and 50% relative humidity, followed by peeling of the remaining length of tape by hand at an angle of 180 degrees. The amount of adhesive residue remaining in each area of the detaped substrate was visually estimated by eye and reported as a percentage of the total taped area for xe2x80x9c93xc2x0 C.xe2x80x9d and xe2x80x9c21xc2x0 C.xe2x80x9d removal, respectively.